28 research outputs found
An Australian childhood obesity summit: the role of data and evidence in 'public' policy making
BACKGROUND: Overweight and obesity in Australia has risen at an alarming rate over the last 20 years as in other industrialised countries around the world, yet the policy response, locally and globally, has been limited. Using a childhood obesity summit held in Australia in 2002 as a case study, this paper examines how evidence was used in setting the agenda, influencing the Summit debate and shaping the policy responses which emerged. The study used multiple methods of data collection including documentary analysis, key informant interviews, a focus group discussion and media analysis. The resulting data were content analysed to examine the types of evidence used in the Summit and how the state of the evidence base contributed to policy-making. RESULTS: Empirical research evidence concerning the magnitude of the problem was widely reported and largely uncontested in the media and in the Summit debates. In contrast, the evidence base for action was mostly opinion and ideas as empirical data was lacking. Opinions and ideas were generally found to be an acceptable basis for agreeing policy action coupled with thorough evaluation. However, the analysis revealed that the evidence was fiercely contested around food advertising to children and action agreed was therefore limited. CONCLUSION: The Summit demonstrated that policy action will move forward in the absence of strong research evidence. Where powerful and competing groups contest possible policy options, however, the evidence base required for action needs to be substantial. As with tobacco control, obesity control efforts are likely to face ongoing challenges around the nature of the evidence and interventions proposed to tackle the problem. Overcoming the challenges in controlling obesity will be more likely if researchers and public health advocates enhance their understanding of the policy process, including the role different types of evidence can play in influencing public debate and policy decisions, the interests and tactics of the different stakeholders involved and the part that can be played by time-limited yet high profile events such as Summits
3/2 Firefighters are not enough
The firefighter problem is a monotone dynamic process in graphs that can be
viewed as modeling the use of a limited supply of vaccinations to stop the
spread of an epidemic. In more detail, a fire spreads through a graph, from
burning vertices to their unprotected neighbors. In every round, a small amount
of unburnt vertices can be protected by firefighters. How many firefighters per
turn, on average, are needed to stop the fire from advancing? We prove tight
lower and upper bounds on the amount of firefighters needed to control a fire
in the Cartesian planar grid and in the strong planar grid, resolving two
conjectures of Ng and Raff.Comment: 8 page
Violator Spaces: Structure and Algorithms
Sharir and Welzl introduced an abstract framework for optimization problems,
called LP-type problems or also generalized linear programming problems, which
proved useful in algorithm design. We define a new, and as we believe, simpler
and more natural framework: violator spaces, which constitute a proper
generalization of LP-type problems. We show that Clarkson's randomized
algorithms for low-dimensional linear programming work in the context of
violator spaces. For example, in this way we obtain the fastest known algorithm
for the P-matrix generalized linear complementarity problem with a constant
number of blocks. We also give two new characterizations of LP-type problems:
they are equivalent to acyclic violator spaces, as well as to concrete LP-type
problems (informally, the constraints in a concrete LP-type problem are subsets
of a linearly ordered ground set, and the value of a set of constraints is the
minimum of its intersection).Comment: 28 pages, 5 figures, extended abstract was presented at ESA 2006;
author spelling fixe
Cyclic projectors and separation theorems in idempotent convex geometry
Semimodules over idempotent semirings like the max-plus or tropical semiring
have much in common with convex cones. This analogy is particularly apparent in
the case of subsemimodules of the n-fold cartesian product of the max-plus
semiring it is known that one can separate a vector from a closed subsemimodule
that does not contain it. We establish here a more general separation theorem,
which applies to any finite collection of closed semimodules with a trivial
intersection. In order to prove this theorem, we investigate the spectral
properties of certain nonlinear operators called here idempotent cyclic
projectors. These are idempotent analogues of the cyclic nearest-point
projections known in convex analysis. The spectrum of idempotent cyclic
projectors is characterized in terms of a suitable extension of Hilbert's
projective metric. We deduce as a corollary of our main results the idempotent
analogue of Helly's theorem.Comment: 20 pages, 1 figur
Bounds on the Complexity of Halfspace Intersections when the Bounded Faces have Small Dimension
We study the combinatorial complexity of D-dimensional polyhedra defined as
the intersection of n halfspaces, with the property that the highest dimension
of any bounded face is much smaller than D. We show that, if d is the maximum
dimension of a bounded face, then the number of vertices of the polyhedron is
O(n^d) and the total number of bounded faces of the polyhedron is O(n^d^2). For
inputs in general position the number of bounded faces is O(n^d). For any fixed
d, we show how to compute the set of all vertices, how to determine the maximum
dimension of a bounded face of the polyhedron, and how to compute the set of
bounded faces in polynomial time, by solving a polynomial number of linear
programs
Infinite-Duration Poorman-Bidding Games
In two-player games on graphs, the players move a token through a graph to produce an infinite path, which determines the winner or payoff of the game. Such games are central in formal verification since they model the interaction between a non-terminating system and its environment. We study bidding games in which the players bid for the right to move the token. Two bidding rules have been defined. In Richman bidding, in each round, the players simultaneously submit bids, and the higher bidder moves the token and pays the other player. Poorman bidding is similar except that the winner of the bidding pays the “bank” rather than the other player. While poorman reachability games have been studied before, we present, for the first time, results on infinite-duration poorman games. A central quantity in these games is the ratio between the two players’ initial budgets. The questions we study concern a necessary and sufficient ratio with which a player can achieve a goal. For reachability objectives, such threshold ratios are known to exist for both bidding rules. We show that the properties of poorman reachability games extend to complex qualitative objectives such as parity, similarly to the Richman case. Our most interesting results concern quantitative poorman games, namely poorman mean-payoff games, where we construct optimal strategies depending on the initial ratio, by showing a connection with random-turn based games. The connection in itself is interesting, because it does not hold for reachability poorman games. We also solve the complexity problems that arise in poorman bidding games
Pivoting in Linear Complementarity: Two Polynomial-Time Cases
We study the behavior of simple principal pivoting methods for the P-matrix linear complementarity problem (P-LCP). We solve an open problem of Morris by showing that Murty’s least-index pivot rule (under any fixed index order) leads to a quadratic number of iterations on Morris’s highly cyclic P-LCP examples. We then show that on K-matrix LCP instances, all pivot rules require only a linear number of iterations. As the main tool, we employ unique-sink orientations of cubes, a useful combinatorial abstraction of the P-LCP